Metals. Most of the elements are metals Good electrical and thermal conductivity Most of them are solids

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1 Metals Most of the elements are metals Good electrical and thermal conductivity Most of them are solids Important structure materials Electric devices Heat: For thermal conduction Heat storage Alloys Energy production (e.g. uranium and plutonium) Catalyst Jewellery

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Iron and Steel Production Iron ores Mineral,

4 Ilmenite, FeTiO 3 Carbonate Siderite, FeCO 3

most important pyrometallurgical process

The most important sources of iron are hematite

Prehistorically, iron was prepared by simply

6 Iron and Steel Production Iron ores Mineral, formula Oxide Hematite, Fe 2 O 3 Magnetite, Fe 3 O 4 Ilmenite, FeTiO 3 Carbonate Siderite, FeCO 3 Sulfide Pyrite, FeS 2 Pyrrhotite, FeS Still the most important pyrometallurgical process economically. The most important sources of iron are hematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ). Prehistorically, iron was prepared by simply heating it with charcoal in a fired clay pot. Today, the reduction of iron oxides to the metal is accomplished in a blast furnace. 6

Separation Cleaning Sintering Reduction of iron-oxides in blast

7 Steps of iron production Mining raw materials Iron ore Limestone Coal Pre-treatment of raw materials Crushing Grinding Separation Cleaning Sintering Reduction of iron-oxides in blast furnace Direct (C) and indirect (CO) Final processing or Steelmaking 7

8 Pyrometallurgy of iron Iron ore, limestone, and coke are added to the top of the furnace. Coke is coal that has been heated in an inert atmosphere to drive off volatile components (~ 80-90% C). Coke has three roles: 1. It is the fuel, producing heat in the lower part of the furnace. 2. It is a reducing agent in the direct reduction (also the source of the reducing gases CO & H 2 ). 3. It remains in the molten iron, alloying it (resulting an iron-carbon mixture). Air is blown into the bottom of the furnace, and combusts with the coke to raise the furnace temp up to 2000 C : 2C(s) + O 2 (g) 2CO(g) H 2 O in the air also reacts with the coke: C(s) + H 2 O(g) CO(g) + H 2 (g) H = -221 kj H = +131 kj Since this reaction is endothermic, if the blast furnace gets too hot, water vapor is added to cool it down without interrupting the chemistry. Limestone (CaCO 3 ) serves as the source of CaO which reacts with silicates & other impurities in the ore to form slag. 8

9 The blast furnace 9

10 Pyrometallurgical process At the top of the furnace, hematite is reduced: 3Fe 2 O 3 (s) + CO(g) 2Fe 3 O 4 (s) + CO 2 (g) Reduction of Fe 3 O 4 occurs further down the furnace (~700 C): Fe 3 O 4 (s) + CO(g) 3FeO(s) + CO 2 (g) Indirect reduction Near the middle of the furnace (1000 C) Fe is produced: FeO(s) + CO(g) Fe(s) + CO 2 (g) Above ~750 C direct reduction by carbon can occur, producing CO for further reduction: 3Fe 2 O 3 (s) + C(s) 2Fe 3 O 4 (s) + CO(g) Fe 3 O 4 (s) + C(s) 3FeO(s) + CO(g) FeO(s) + C(s) Fe(s) + CO(g) Molten iron is produced lower down the furnace & removed. Slag is less dense than iron & can be drained away. The iron formed (called pig iron) still contains around 4-5% C, % Si, % Mn + S and P and needs to be further processed. 10

11 Slag Most rocks are composed of silica (SiO 2 ) and silicates (SiO 3 2- ) & are almost always present in the ore. These compounds don t melt at the furnace temperature & would eventually clog it up. An important chemical method to remove these is using a flux that combines with silica & silicates to produce a slag. Slag collects at the bottom of the furnace, above the molten metal and does not dissolve in the molten metal. The heat of the furnace decomposes the limestone to calcium oxide (as in a calcination reaction). CaO (a basic oxide) reacts with silicon dioxide and produces calcium silicate. At around 250 C (top of the furnace), limestone is calcinated: CaCO 3 (s) CaO(s) + CO 2 (g) CaO(s) + SiO 2 (s) CaSiO 3 (l) Slag helps to protect the molten iron from re-oxidation (Inhibits the contact with the air blown in the furnace). Slag is used in road making, and can also be combined with cement. 11

12 Reactions in the blast furnace 12

13 The product of the blast furnace The iron formed in a blast furnace is called pig iron generally containing 3 4% C, % Si, 0.5 1% Mn, % P, and % S The solid metal obtained from liquid pig iron is called cast iron Cast iron is wrought by hammering at o C Most iron is converted to alloys known collectively as steel Cast Iron White: Hard and brittle, good wear resistance Uses: rolling & crunching equipment Grey: Good compressive & tensile strength, machinability, and vibration-damping ability Uses: machine bases, crankshafts, furnace doors, Engine Blocks 13

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15 Pig iron is brittle, and not directly very useful as a material. The oxidation of carbon-, phosphorous-, silicium- and manganese content to the required amount,is called steelmaking Steelmaking There are different processes for steel production: Siemens-Martin process (Open-hearth furnace): using scrap metal as oxidizing agent, gas-burners for heating Converters: using air or oxigen as oxidizer: Bessemer Thomas LD Electro-steel: electric arc provides the heat for the reaction 15

Basic oxygen steelmaking (Linz-Donawitz- steelmaking) The impurities are removed by oxidation in a vessel called a converter. The oxidising agent is pure O 2 or O 2 mixed with Ar.

16 Basic oxygen steelmaking (Linz-Donawitz- steelmaking) The impurities are removed by oxidation in a vessel called a converter. The oxidising agent is pure O 2 or O 2 mixed with Ar. Air cannot be used as N 2 reacts with iron to form iron nitride which is brittle. O 2 blown directly into molten metal. Reacts exothermically with C, Si, P, Mn. The heat keeps the iron in molten state. C & S expelled as CO and SO 2 gas. Si oxidised to SiO 2 & incorporates into the slag layer. Once oxidation complete, contents poured out & various alloying elements added to produce steels. 16

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19 Types of iron & steel Wrought iron iron with all the C removed. Soft & easily worked with little structural strength. No longer produced commercially. Mild steel iron containing around 0.25% C. Stronger & harder than pure iron. Has many uses including nails, wire, car bodies, girders & bridges, etc. High carbon steel contains around 1.5% C. Very hard, but brittle. Used for things like cutting tools, and masonry nails. Stainless steel iron mixed with chromium and nickel. Resistant to corrosion. Uses include cutlery, cooking utensils, kitchen sinks, etc. Titanium steel iron mixed with titanium. Withstands high temperatures. Uses include gas turbines, spacecraft parts, etc. Manganese steel iron mixed with manganese. Very hard. Uses include rockbreaking machinery, military helmets, etc. 19

Stainless steel Steel alloyed with chromium (18%), nickel (8%), magnesium (8%). Hard and tough. Corrosion resistance. Comes in different grades. Sinks, cooking utensils, surgical instruments.

20 Stainless steel Steel alloyed with chromium (18%), nickel (8%), magnesium (8%). Hard and tough. Corrosion resistance. Comes in different grades. Sinks, cooking utensils, surgical instruments. Ferritic chromium: very formable, relatively weak; used in architectural trim, kitchen range hoods, jewelry, decorations, utensils Grades 409, 430, and other 400 Austentitic nickel-chromium: non-magnetic, machinable, weldable, relatively weak; used in architectural products, such as fascias, curtain walls, storefronts, doors & windows, railings; chemical processing, food utensils, kitchen applications. series. Grades 301, 302, 303, 304, 316, and other 300 series. Martensitic chromium: High strength, hardness, resistance to abrasion; used in turbine parts, bearings, knives, cutlery and generally Magnetic. Grades 17-4, 410, 416, 420, 440 and other 400 series Maraging (super alloys): High strength, high Temperature alloy used in structural applications, aircraft components and are generally magnetic. Alloys containing around 18% Nickel. High Speed Steel Medium Carbon steel alloyed with Tungsten, chromium, vanadium. Very hard. Resistant to frictional heat even at high temperature. Can only be ground. Machine cutting tools (lathe and milling). Drills 20

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22 Final processing of steel 22

Alternatives for iron production The thermite reaction Aluminium metal can reduce Iron(III) oxide (Fe 2 O 3 ) in a highly exothermic reaction. Molten iron is produced at around 3000 C.

23 Alternatives for iron production The thermite reaction Aluminium metal can reduce Iron(III) oxide (Fe 2 O 3 ) in a highly exothermic reaction. Molten iron is produced at around 3000 C. Reaction used for thermite welding, often used to join railway tracks. Fe 2 O 3 (s) + 2Al(s) 2Fe(s) + Al 2 O 3 (s) Electrowinning of iron (The Pyror process): Studies into iron extraction by electrowinning from sulphate solutions were first carried out around 50 years ago, then subsequently forgotten. May become important again in the future as new, more environmentally friendly methods are sought for steelmaking. 23

24 Electrowinning of iron The Pyror process: First step is to convert iron pyrite (FeS 2 ) into an acid soluble form (FeS). Achieved by either calcining at 800 to 900 C to expel a loosely-bound S, or by smelting in an electric furnace. Step 2 is a leaching step using H 2 SO 4 to extract iron from FeS: FeS(s) + H 2 SO 4 (l) FeSO 4 (l) + H 2 S(g) Step 3: before entering the electrowinning cells, the solution is purged with air to remove any remaining H 2 S. Step 4: Electrolysis. Iron is reduced and deposited on the cathode, while O 2 is evolved, and H 2 SO 4 is regenerated at the anode. More specifically: Fe e - Fe(s) 2H + + 2e - H 2 (g) Fe 3+ + e - Fe 2+ SO H 2 O H 2 SO 4 + 1/2O 2 + 2e - Fe 2+ Fe 3+ + e - 24

25 Electrowinning of iron The process was shown to be quite efficient. During a 2 year pilot-plant project, a quantity of iron close to 150 tonnes was produced. Electrolysis was run for several weeks before stripping was performed, resulting in deposits of 13mm or more in thickness. 25

26 Aluminium production Distributed in Earth s crust (~8%), in oxide form (Al 2 O 3 ) bauxite, kaolinite, nefelin and alunit mineral. 26

27 The brief history of aluminium production 27

28 Bauxite - typical composition Bauxite is the most important aluminous ore for the production of alumina. Bauxite occurs close to the surface in seams varying from one meter to nine meters, formed as small reddish pebbles (pisolites). Bauxite contains 40 to 60 mass% alumina combined with smaller amounts of silica, titania and iron oxide. 28

then calcined to aluminium oxide. A Bayer Process plant is principally a device for heating and cooling a large re circulating stream of caustic soda solution.

29 Bayer process Alumina is mainly extracted from bauxite using Bayer Process. The Bayer process dissolves the aluminium component of bauxite ore in sodium hydroxide (caustic soda); removes impurities from the solution; and precipitates alumina tri hydrate, which is then calcined to aluminium oxide. A Bayer Process plant is principally a device for heating and cooling a large re circulating stream of caustic soda solution. Bauxite is added at the high temperature point, red mud is separated at an intermediate temperature, and alumina is precipitated at the low temperature point in the cycle. Alumina (aluminium oxide Al 2 O 3 ) obtained is a fine white material similar in appearance to salt. Alumina is also used in abrasive, ceramics and refectory industries. 29

30 Bauxite - typical minerals 30

The Bayer process Red Mud Component Range Fe 2 O 3 30 60% Al 2

31 The Bayer process Red Mud Component Range Fe 2 O % Al 2 O % SiO % Na 2 O 2 10% CaO 2 8% TiO 2 Trace - 10% 31

32 The Bayer chemistry For precipitation readily available Al-hydroxide crystals can be added to start precipitation. Growing crystals is less energy demanding than crystal creation in some cases 32

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34 Aluminium Production Technology The Hall- Heroult process is an example of Aluminium smelting process and is used industrially. Aluminium cannot be produced by an aqueous electrolytic process because hydrogen is electrochemically much nobler than aluminium. Thus, liquid aluminium is produced by the electrolytic reduction of alumina (Al 2 O 3 ) dissolved in an electrolyte (bath) mainly containing Cryolite (Na 3 AlF 6 ). The overall chemical reaction can be written as: 2 Al 2 O 3 (dissolved) +3C (s) =4 Al (l) +3 CO 2 (g) (1) 34

Cryolite - Cryolite is the main constituent of the electrolyte used in alumina electrolysis. Chemically it is Na 3 AlF 6, a double fluoride of sodium and aluminium. It is a white granular powder.

35 Cryolite - Cryolite is the main constituent of the electrolyte used in alumina electrolysis. Chemically it is Na 3 AlF 6, a double fluoride of sodium and aluminium. It is a white granular powder. Certain impurities may give it a grey or pink discoloration. The freezing point of cryolite is 1009 C. Synthetic Cryolite is made from fluorspar (CaF 2 ), which is found as a natural mineral. Fluorspar is treated with sulphuric acid to produce hydrofluoric acid HF. CaF 2 +H 2 SO 4 = 2HF (g) +CaSO 4 (s) HF is then reacted with sodium oxide Na 2 O and alumina to produce cryolite. A modern aluminum reduction cell, commonly called a pot, is made of a rectangular steel shell, (At Balco m long by m wide by 1.372m high), lined with refractory thermal insulation. Inside the shell there is an inner lining of SiC to contain the highly corrosive molten fluoride electrolyte (or bath, as it is commonly called) and liquid aluminum. Electric current enters the cell through 40 prebaked carbon anodes. A crust of frozen bath and alumina covers the molten bath. Alumina in the Cell is fed through point feeders. Thermal insulation is designed to provide sufficient heat loss to maintain a protective ledge of frozen electrolyte on the walls of cells, but not on the bottom under the anodes. 35

36 Illustrations of Prebake (Hall-Heroult, left) and Söderberg (right) cells for aluminium smelting 36

37 There are two basic technology- Prebaked Technology and Soderberg Technology. RAW MATERIAL FOR ALUMINIUM PRODUCTION The major raw material required for aluminium production is alumina, carbon, power, aluminium fluoride and cryolite. 37

38 GHGs from Primary Aluminium Production Electricity Input 15.6 MWh/t Al t CO2/t Al IAI average = 5.8 Alumina Production t CO 2 eq/t Al IAI average = 1.9 Gases Feeder Anode Electrolyte Molten Aluminium Cathode Block PFC Generation t CO 2 eq/t Al Global average = 1.26 Anode Carbon t CO 2 eq/t Al IAI average = 2.0 Source: IAI Life Cycle Inventory D IAI 2003 PFC Survey GHG from Primary Aluminium Production Two PFC (perfluorocarbon compounds - CF 4 and C 2 F 6 ) contribute about 40% of direct primary aluminium GHG emissions 38

39 Inventory for world average production of 1,000 kg primary aluminium Building and Construction Transportation Electrical engineering Packaging Other applications 39

- Early human use (8000 BC) - Heat exchangers (good

(chalcopyrite and chalcocite) - Copper carbonates

40 - Early human use (8000 BC) - Heat exchangers (good thermal conductivity) - Elecric applications (good electric conductivity) - Catalyst - Coins - Alloys (brass, bronze) - Native copper - Copper sulfides (chalcopyrite and chalcocite) - Copper carbonates (azurite and malachite) - Copper oxide (cuprite) Copper production 40

Smelting process - Crushing of ores - Concentration by froth flotation Mixing the ore

Bathed in water with foaming agent and air is shot up to form bubbles.

- Roasting At 500-700 C most of the sulfur is burnt as sulfide gas.

41 Smelting process - Crushing of ores - Concentration by froth flotation Mixing the ore reagents to make copper hydrophobic. Bathed in water with foaming agent and air is shot up to form bubbles. The froth is skimmed off. Other impurities like Mo, Pb, Au, Ag can be processed. - Roasting At C most of the sulfur is burnt as sulfide gas. 2CuFeS 2 + 6,5O 2 = 2CuO + Fe 2 O 3 + 4SO 2 CuFeS 2 + 4O 2 = CuSO 4 + FeSO 4 Exothermic reactions. At 1200 C silica and limestone forms slag with iron-oxides can be removed from surface. 41

The anodes are immersed to copper sulfate and sulfuric acid with a prepared pure copper cathode (or stanless steel).

42 Smelting process Further reaction with oxygen in converter: CuS2 + O2 = 2 Cu + SO2 Molten copper asborbs certain amounts of sulfur and oxygen. Blister copper has 97-99% copper content. The remaining is oxygen and sulfur. Electrolytic refining Copper is casted to anodes. The anodes are immersed to copper sulfate and sulfuric acid with a prepared pure copper cathode (or stanless steel). As current is introduced, copper ions start to migrate to the cathode. 85% of the worlds copper is produced by smelting. 42

Leaching (Hydrometallurgic process) The remaining 15% is prepared by leaching process. The ores usually have less copper-content. Oxides, sulfides and mixed ores can be processed.

43 Leaching (Hydrometallurgic process) The remaining 15% is prepared by leaching process. The ores usually have less copper-content. Oxides, sulfides and mixed ores can be processed. For oxydes sulfuric acid is applied as leaching agent. Solvent extraction is applied to achieve copper-rich solution. Organic solvents or extractants are used. Copper ions are exchanged to hydrogen ions acid is regenerated. The copper-rich solution is used in electrowinning. 43

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5072 CHEMISTRY (NEW PAPERS WITH SPA) TOPIC 9: METALS 5067 CHEMISTRY (NEW PAPERS WITH PRACTICAL EXAM) TOPIC 9: METALS

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